Connection arrangements of this type are well known for interconnecting pipelines for supplying and receiving fluid between two stations, one of which could be a fixed station such as an offshore mooring point and the other of which could be a mobile station, such as a hydrocarbon tanker. Known connection and disconnection arrangements are provided with an emergency disconnection device making it possible, in an extreme situation of drift or accident—for example in case of fire—to distance the mobile pipe section from the fixed pipe section in order to prevent damage to the structure or wrenching off of the pipes, while ensuring containment of the fluid in the pipelines.
In the known arrangements, the pivot axes of the valve disks of the two interconnected pipe sections are spaced apart from one another in the axial direction of the pipe sections. When these disks assume their closed positions they delimit between them a relatively large space that is filled with fluid. In the event of emergency disconnection, this quantity of fluid is lost to the environment. Such an incident may cause pollution of the environment or involve a risk of fire. This is the case in particular for the transfer of liquefied natural gas (LNG) between, for example, a loading or unloading terminal and a liquefied gas tanker.
In the past, many different types of valves have been used in various environments and applications to control the flow of fluids through a pipeline, conduit, or the like. Linear valve types include valves such as globe valves, gate valves and diaphragms, whereas quarter turn valve types include butterfly valves, ball valves and plug valves. These valves can be manually operated or can be actuated and modulating, depending on the specific application. Gate valves, plug valves, wedge valves and ball valves, for example, have all found their respective niches in the art of fluid flow control. It is of primary importance for such valves to provide for substantially leak-free operation; it is especially so for valves regulating the flow of high pressure fluids or potentially hazardous fluids such as highly flammable or caustic substances. Ease of operation, that is, opening and closing, is sometimes as important a feature of a valve, particularly a high pressure valve, as leak-free operation. If a valve cannot be operated quickly and with relatively little effort, besides the wear and tear on the valve parts, the excess time and effort spent in operating the valve and the related inconvenience associated with such a high torque valve can lead to other adverse consequences. Thus it is clearly desirable and advantageous to employ valves that are both reliable, that is, leak proof, and fast and easy to operate, preferably requiring very low torque attainable with only hand or light tool application.
An example of an arrangement for connecting and disconnecting two pipe sections of a fluid transfer system is found in U.S. Pat. No. 6,877,527 where each section includes a butterfly valve with a disk pivotally mounted inside, rotating about a swivel axis between a closed position closing the cross-section of the fluid flow and an open position opening the cross-section of the fluid flow. The swivel axes extend perpendicular to the pipe axis and parallel to each other. This configuration involves for each valve an actuating mechanism and is relatively complex and heavy. Although the known construction reduces the amount of fluid trapped when connection of the pipe sections occurs, it fails to prevent any fluid from staying trapped once the connection is realized.
An example of a cam actuated split ball valve is found in U.S. Pat. No. 5,265,845 where the split ball halves are pivotably mounted to the head member to be pivotable about the mounting means alternately to separate the halves from one another or to collapse them toward one another. The closure member is rotatable with the stem and head member alternately to place the flow port portions in register with the seats to open the valve, or to align the sealing surfaces with the seats to close the valve. An actuating cam is disposed in the valve body between the split ball halves for alternately forcing them apart or permitting them to collapse toward one another and away from sealing engagement with the seats. This arrangement retains its ease of operation and low operating torque at very high working pressures but it does not permit any disconnection of the pipe sections that are attached to the valve.
Another connecting device for conduits is described in U.S. Pat. No. 4,335,747, disclosing in each conduit a spherical valve element having a diametrically extending through-hole. In one pipe section, the mating surface of the housing in which the spherical element is seated is formed with an opening through which a part of the valve element projects. On the other conduit, the spherical valve element does not project beyond the mating surface of the housing but is formed with a part-spherical recess for receiving the projected portion of the valve element in the first ball valve assembly. In this way inclusion of air can be prevented upon interconnecting the two pipe sections, which is especially advantageous in cryogenic applications. Each ball valve however is driven by individual actuating members, making the construction relatively complex and heavy.
An emergency shut-off device is described U.S. Pat. No. 5,305,776, wherein two valves each have an obturator pivotable in the pipe body around parallel pivot axes, so that it can assume a shut-off position transversely to the length direction of the pipe and an open position substantially perpendicular to its shut-off position. Each obturator has an engagement device for engaging the obturator of the other valve fixing the two obturators in a contiguous arrangement in their open positions, which they assume normally, and releasing the obturators so that they can assume their shut-off configurations when the valves move apart because the joint has been subjected to loads equal to or greater than the breaking load. This arrangement has to be changed after each emergency shut-off as the means joining the two obturators have to be broken to separate the obturators.
It is an object of the present invention to overcome the problems discussed above. It is in particular an object of the invention to provide a valve assembly which can be connected and disconnected repeatedly while avoiding leakage. It is in particular an object of the invention to provide a valve assembly which is of a simple and light-weight construction and which is easy to operate.